Electrolytic copper foil with carrier foil and copper-clad laminate using the electrolytic copper foil with carrier foil

ABSTRACT

An object of the present invention is to reduce and to stabilize peel strength of a carrier foil in an electrodeposited copper foil with carrier employing an organic adhesive interface, thereby facilitating peeling of the carrier foil. The electrodeposited copper foil with carrier of the present invention contains a carrier foil layer, an organic adhesive interface layer formed on the carrier foil layer, and an electrodeposited copper foil layer formed on the organic adhesive interface layer, wherein the difference between the coefficient of thermal expansion of material forming the carrier foil layer at a certain temperature and that of material forming the electrodeposited copper foil at the same temperature is 4×10 −7 /deg.C or more.

TECHNICAL FIELD

The present invention relates to electrodeposited copper foil withcarrier predominantly employed for producing printed wiring boards.

BACKGROUND ART

Conventionally, electrodeposited copper foil with carrier has beenemployed as a material for producing printed wiring boards, which arewidely used in the electric and electronic industries. In general,electrodeposited copper foil with carrier is bonded, throughhot-pressing, onto an electrically insulating polymer material substratesuch as glass-epoxy substrate, phenolic polymer substrate, or polyimide,to thereby form a copper-clad laminate, and the thus-prepared laminateis used for producing printed wiring boards of high density mounting.

In hot-pressing, a copper foil, a prepreg (substrate) which is curedinto a B-stage, and mirror plates serving as spacers are laid-up in amultilayered manner, and the copper foil and the prepreg arehot-press-bonded at high temperature and pressure (hereinafter the stepmay be referred to as “press-forming”). When wrinkles are in turngenerated in the copper foil to be pressed, cracks are generated in thewrinkled portions, thereby possibly causing bleeding of resin from aprepreg, or open circuit of a formed electric circuit during an etchingstep followed in production steps of printed wiring boards. In anelectrodeposited copper foil with carrier, the carrier foil preventsgeneration of wrinkles in the electrodeposited copper foil.

Electrodeposited copper foils with carrier are generally divided intotwo types; i.e., foils with peelable carriers and foils with etchablecarriers. Briefly, the difference between the two types of foils lies inthe method for removing the carrier after completion of press-forming.In foil with peelable carrier, the carrier is removed by peeling,whereas in foil with etchable carrier, the carrier is removed byetching. The present invention is directed to electrodeposited copperfoil with peelable carrier.

However, the peel strength of conventional peelable carriers aftercompletion of press-forming varies considerably, and a preferablestrength of 50-300 gf/cm is generally required. In some cases, a carrierfoil cannot be removed from the copper foil. Thus, conventional peelablecarriers have a drawback; i.e., target peel strength is difficult toattain. The drawback prevents the widespread use of the electrodepositedcopper foil with carrier employed for general use.

Causes of variation in peel strength of a carrier foil will next bedescribed. Conventional electrodeposited copper foil with carrier,regardless of whether the carrier is peelable or etchable, has ametallic—e.g., zinc-containing—adhesive interface layer between thecarrier foil and the electrodeposited copper foil. The amount of metalcomponents forming the adhesive interface layer determines, with slightdependence on the type of the carrier foil, whether the formed copperfoil with carrier has peelable carrier foil or etchable carrier foil.

In many cases, such a metallic adhesive interface layer is formedelectrochemically; i.e., through electrodeposition by use of a solutioncontaining a predetermined metallic element. However, inelectrodeposition, controlling the amount of deposition on a very minutescale is difficult, and reproduction of the deposition is unsatisfactoryas compared with other methods for forming the adhesive interface layer.In addition, the boundary line of the required deposition amountdetermining whether the formed carrier becomes peelable or etchable isdifficult to adjust; i.e., small variations in amount of a metalliccomponent contained in the adhesive interface layer determine the typeof the carrier. Thus, stable peeling performance may be difficult toattain.

From another point of view, such a carrier foil is removed by peelingafter completion of press-forming, typically at a temperature as high as180° C. under high pressure for 1 to 3 hours. Components contained inthe carrier foil and copper atoms contained in the electrodepositedcopper foil may be mutually diffused through the adhesive interfacelayer. Such mutual diffusion strengthens the adhesion, thereby failingto attain moderate peel strength.

In order to solve the aforementioned drawbacks, the present inventorshave proposed electrodeposited copper foil with carrier in which theadhesive interface layer between the carrier foil layer and theelectrodeposited copper foil comprises an organic agent such as CBTA,and a method for producing the electrodeposited copper foil withcarrier.

The aforementioned electrodeposited copper foil with carrier which thepresent inventors have proposed completely solves the drawback that thecarrier foil cannot be peeled; i.e., the proposed foil can be peeled ata strength of 3-200 gf/cm. However, there has been still increasingdemand for a copper foil which can be peeled with a moderate andconstant peel strength after a copper-clad laminate is produced by useof an electrodeposited copper foil with carrier.

Meanwhile, an advantage of electrodeposited copper foil with carrier perse is the state where one surface of the carrier foil are placed as ifit were bonded in a lamination manner to one surface of anelectrodeposited copper layer. In other words, the electrodepositedcopper foil with carrier can prevent staining the surface of theelectrodeposited copper foil with foreign matter and damaging theelectrodeposited copper foil layer by maintaining the bonding state atleast immediately before an etching step for forming printed circuits,which step is carried out after production of a copper-clad laminatethrough hot-pressing the electrodeposited copper foil with carrier and aprepreg (substrate).

Thus, separation of a carrier foil and an electrodeposited copper foilduring handling of the electrodeposited copper foil with carrier beforehot-press-forming is not acceptable. Although the carrier foil must bepeeled with a moderate peel strength after completion of hot-pressing,lamination-type bonding of the carrier foil to one surface of anelectrodeposited copper foil of a copper-clad laminate must also bemaintained, at least immediately before an etching step so as to preventcontamination and staining the surface of the copper clad laminate withforeign matter.

SUMMARY OF THE INVENTION

In view of the foregoing, the present inventors have conducted extensivestudies, and have concluded that the peel strength between a carrierfoil and an electrodeposited copper foil should be controlled to 3 gf/cmto 100 gf/cm so as to maintain lamination-type bonding of the carrier toone surface of the electrodeposited copper foil at least immediatelybefore an etching step with lower peel strength.

Thus, the aforementioned demands can be satisfied by selectingcombination of materials of a carrier foil and an electrodepositedcopper foil, which materials are predominant materials for forming anelectrodeposited copper foil with carrier. This approach differs fromthe approach of modifying an organic agent which is employed in anadhesive interface layer and the approach of improving interface-formingtechniques, such as a method for forming the adhesive interface layer.Since an electrodeposited copper foil with carrier is hot-pressed duringproduction of a copper-clad laminate, the copper foil with carrier issubjected to a certain amount of thermal stress. The present inventorshave found that, among properties of the materials, coefficient ofthermal expansion is an important factor. The present invention has beenaccomplished on the basis of this finding.

Accordingly, the present invention provides an electrodeposited copperfoil with carrier comprising a carrier foil layer, an organic adhesiveinterface layer formed on the carrier foil layer, and anelectrodeposited copper foil layer formed on the organic adhesiveinterface layer, wherein the difference between the coefficient ofthermal expansion of material forming the carrier foil layer at acertain temperature and that of material forming the electrodepositedcopper foil at the same temperature is 4×10⁻⁷/deg.C or more.

After careful studies, the present inventors have found that a carrierfoil of the electrodeposited copper foil with peelable carrier employedfor producing copper-clad laminates can be peeled considerably easilywhen the difference between the coefficient of thermal expansion ofmaterial forming the carrier foil layer at a certain temperature andthat of material forming the electrodeposited copper foil at the sametemperature is 4×10⁻⁷/deg.C or more. Thus, the invention is based onthis finding. When the carrier foil layer and the electrodepositedcopper foil layer are subjected to heat hysteresis and the two layersexhibit identical thermal expansion behavior, the bonding conditionsbetween the two layers via the organic adhesive interface layer aremaintained within an elastic limit. Under such conditions, peeling atthe organic adhesive interface layer is not promoted. However, when thedifference between the coefficient of thermal expansion of materialforming the carrier foil layer at a certain temperature and that ofmaterial forming the electrodeposited copper foil at the sametemperature is 4×10⁻⁷/deg.C or more, thermal stress for causing shear ofthe two layers at the organic adhesive interface is generated by heathysteresis, which typically occurs during a process for producingcopper-clad laminates. Thus, the two layers can be peeled from eachother much more easily. When the difference between the coefficient ofthermal expansion of material forming the carrier foil layer at acertain temperature and that of material forming the electrodepositedcopper foil at the same temperature is controlled to 4×10⁻⁷/deg.C ormore, the peel strength can be controlled to 3-100 gf/cm, which is atarget peel strength in the present invention. The difference, i.e.,4×10⁻⁷/deg.C or more, may be applied in either case of expansion orshrinkage of the carrier foil with respect to the electrodepositedcopper foil.

In the present invention, the range “4×10⁻⁷/deg.C or more” does notrefer to a range in which the upper limit remains uncertain. This isbecause, given a material forming the carrier foil layer and atemperature at which the foil is treated, a specific upper limit of thedifference between a coefficient of thermal expansion of materialforming the carrier foil layer and that of material forming theelectrodeposited copper foil is univocally determined.

In the electrodeposited copper foil with carrier of the invention, anorganic adhesive interface layer is formed on a carrier foil layer andan electrodeposited copper foil layer is formed on the organic adhesivelayer. Accordingly, the organic agent adheres to both the carrier foillayer and the electrodeposited copper foil layer, and the layercontaining the organic layer also serves as an adhesive interface layer.When an appropriate organic agent is employed in the adhesive interfacedisposed between the carrier foil layer and the electrodeposited copperfoil layer, peeling behavior of the carrier foil layer and theelectrodeposited copper layer caused by difference in coefficient ofthermal expansion is relaxed, even though the electrodeposited copperfoil with carrier is subjected to certain thermal impact during aprocess for producing copper-clad laminates. Accordingly, spontaneouspeeling of the carrier foil layer and the electrodeposited copper layeris considered to be prevented.

In the present invention, the electrodeposited copper foil with carrierhas a schematic cross-sectional structure as shown in FIG. 1.Specifically, one surface of the carrier foil layer (hereinafter may besimply referred to as “carrier foil”) is placed as if it were boned in alaminated manner to one surface of the electrodeposited copper layer(hereinafter may be simply referred to as “electrodeposited copperfoil”) via the organic adhesive interface layer. Typically, such aselectrodeposited copper foil with carrier and a prepreg (e.g., FR-4substrate) or an internal printed wiring board—the prepreg and theinternal printed wiring board serving as insulating layers—arelaminated, and the resultant laminate is press-formed in an atmosphereat approximately 180° C., to thereby obtain a copper-clad laminate.

In the present invention, either organic material or inorganic metallicmaterial may be used to form the carrier foil which is combined with anelectrodeposited copper foil, so long as the difference in coefficientof thermal expansion is 4×10⁻⁷/deg.C or more. However, as described inthe invention, an electrodeposited copper foil is advantageouslyemployed, in view of ease of recycling the foil and stable productionthereof. In this case, although the electrodeposited copper foil and thecarrier foil of the electrodeposited copper foil with carrier of thepresent invention are both electrodeposited copper foils, copper foilshaving different physical properties, particularly coefficient ofthermal expansion, must be combined.

In order to provide better understanding of the following description,types of electrodeposited copper foils will next be described. Althoughthere are a variety of international standards regarding theclassification of electrodeposited copper foils, classification on thebasis of the most widely employed standards; i.e., IPC (The Institutefor Interconnecting and Packaging Electronic Circuits) standards, willbe described.

According to the IPC standards, electrodeposited copper foils areclassified as Grade 1 to Grade 3 on the basis of basic physicalproperties such as elongation and tensile strength. Copper foildesignated by Grade 1 is standard electrodeposited copper foil, andcopper foil designated by Grade 2 is high ductility electrodepositedcopper foil. These days, among persons having ordinary skill in the art,electrodeposited copper foils belonging to Grades 1 and 2 are generallycalled standard electrodeposited copper foils (hereinafter these copperfoils are referred to as “standard electrodeposited copper foils”).Electrodeposited copper foil belonging to Grade 3 is generally calledHTE foil. HTE foil generally refers to copper foil exhibiting hightemperature elongation of 3% in an atmosphere at 180° C. HTE foil iscompletely different from standard copper foils belonging to Grades 1and 2, since the standard copper foils exhibit a high temperatureelongation less than 2%.

In recent manufacture of printed wiring board, copper foils belonging toGrade 3 are further classified clearly into two categories; i.e.,electrodeposited copper foils exhibiting a high temperature elongationof approximately 3% to 18% (hereinafter simply referred to as HTE foils)and electrodeposited copper foils exhibiting a high temperatureelongation of approximately 18% to 50% (throughout the presentdescription, these foils are simply referred to as S-HTE foils). Thesetwo types of foils are employed in accordance with purposes of use.

The basic difference between HTE foil and S-HTE foil lies incharacteristics of deposited crystals, even though these two foilscomprise electrodeposited copper having a purity of approximately99.99%. During a process for producing copper-clad laminates, anelectrodeposited copper foil is hot-pressed so as to be laminated with asubstrate by heating at 180° C. for approximately 60 minutes. Throughobservation under an optical microscope of the metallographic structureof the foils after completion of heating, no recrystallization isobserved in HTE foil, but recrystallization is observed in S-HTE foil.

The difference is considered to be due to production conditions of thefoils. Briefly, production conditions during electrolysis, such ascomposition of a solution, concentration of a solution, a method forfiltering a solution, solution temperature, additives, and currentdensity, are modified in order to control physical properties of copperfoils. This may cause variation in crystallographic properties ofdeposited crystals. Particularly, the more easily recrystallizationoccurs, the more dislocations are accumulated in crystals. Thedislocations are immobilized tightly, and immediately undergorearrangement by application of a small amount of heat, thereby possiblycausing recrystallization readily.

The IPC standards also include classification of copper foils fromanother aspect; i.e., surface profile (roughness) of copper foil whichis laminated with a substrate to produce copper-clad laminates. Theclassification is determined by surface roughness obtained in accordancewith the IPC-TM-650 test method. Specifically, copper foils arecategorized into three types: standard profile foil (S type) having noparticular specified roughness; low profile foil (L type) having amaximum roughness of 10.2 μm or less; and very low profile foil (V type)having a maximum roughness of 5.1 μm or less.

Among them, when a copper foil belonging to V type, setting aside S typeor L type, is produced by electrolysis, the amounts of impurities in anelectrolytic solution must be lowered and conditions for electrolysismust be particularly tailored. The grain size of deposited crystals mustbe reduced to a considerably small size such that the grains cannot beobserved under an optical microscope having a magnification of some 100times, as compared with columnar deposits typically observed under anoptical microscope. Thus, electrodeposited copper foil belonging to Vtype has very fine crystal grains, and such metallographic structure iscompletely different from that of other copper foils. The fine crystalgrains provide high tensile strength and hardness.

The aforementioned difference in metallographic characteristic providesdifference in physical properties of copper foil, and coefficient ofthermal expansion varies to a small deg.C in accordance with theaforementioned types of copper foils. Therefore, when anelectrodeposited copper foil endowed with appropriate physicalproperties; particularly, appropriate coefficient of thermal expansion,is employed as a carrier foil of electrodeposited copper foil withcarrier, the coefficient of thermal expansion can be controlled to avalue different from that of an electrodeposited copper foil of theelectrodeposited copper foil with carrier.

In the present invention, the electrodeposited copper foil belonging toGrades 1 to 3 of the IPC standards and for forming the carrier foillayer refers to the aforementioned standard electrodeposited copperfoil, HTE foil, and S-HTE foil. The material for forming theelectrodeposited copper foil layer is a copper foil having very finecrystal grains and categorized into very low profile type (V type) ofthe IPC standards. Coefficient of thermal expansion (α) of these copperfoils were measured, and the results are shown in Table 1. In Table 2,absolute values of the difference between coefficient of thermalexpansion (α) of an electrodeposited copper foil layer and that (α) of acarrier foil layer are summarized. Coefficient of thermal expansion wasmeasured by means of a thermo-mechanical analyzer, TMA standard typeCN8098F1 (product of Rigaku Denki).

TABLE 1 Coefficient of thermal expansion (α) × 10⁻⁵ MeasuringElectrodeposited Carrier foil layer temperature Cu foil layer Standard °C. V type HTE S-HTE copper foil Elevating 50 1.355 0.969 1.395 1.453 1001.491 1.137 1.527 1.689 150 1.601 1.411 1.649 1.860 200 1.594 1.7341.654 1.939 Lowering 150 1.649 1.757 1.595 2.264 100 1.523 1.820 1.4812.261 50 1.515 2.240 1.477 4.637

TABLE 2 Difference in coefficient of thermal expansion (α) × 10⁻⁵Absolute value of (electrodeposited Cu foil layer) − (carrier foillayer) Measuring (V type) − temperature (V type) − (V type) − (standard° C. (HTE) (S-HTE) Cu foil) Elevating 50 0.386 0.040 0.098 100 0.3540.036 0.198 150 0.190 0.048 0.259 200 0.140 0.060 0.345 Lowering 1500.108 0.054 0.615 100 0.297 0.042 0.738 50 0.725 0.038 3.122

Calculated absolute values of (α of electrodeposited copper foillayer)−(αof carrier foil) are shown in Table 2. When S-HTE foil isemployed as a carrier foil, the average absolute value of the differencein coefficient of thermal expansion is 0.046×10⁻⁵/deg.C in thetemperature-elevating step and 0.049×10⁻⁵/deg.C in thetemperature-lowering step. When HTE foil is employed as a carrier foil,the average absolute value of the difference in coefficient of thermalexpansion is 0.268×10⁻⁵/deg.C in the temperature-elevating step and0.318×10⁻⁵/deg.C in the temperature-lowering step. When standardelectrodeposited copper foil belonging to Grade 1 is employed as acarrier foil, the average absolute value of the difference incoefficient of thermal expansion is 0.225×10⁻⁵/deg.C in thetemperature-elevating step and 1.205×10⁻⁵/deg.C in thetemperature-lowering step.

When the carrier foil layer and the electrodeposited copper foil layerare subjected to heat hysteresis and the two layers exhibit identicalthermal expansion behavior, the bonding conditions between the twolayers via the organic adhesive interface layer are maintained within anelastic limit. Under such conditions, peeling at the organic adhesiveinterface layer is not promoted. Briefly, the greater the difference incoefficient of thermal expansion, the more easily peeling occurs due tothermal expansion, and the smaller the difference in coefficient ofthermal expansion, the more difficult peeling is. In order to elucidatethe relationship between coefficient of thermal expansion and peelstrength, the data must be compared in the aforementioned temperaturerange. The difference in coefficient of thermal expansion must be4×10⁻⁷/deg.C or more. As is clear from Table 2, the difference incoefficient of thermal expansion is smaller in the temperature-elevatingstep than in the temperature-lowering step. Accordingly, whenever thecoefficient of thermal expansion falls within the above range in thetemperature-elevating step, it is considered to fall within the aboverange also in the temperature-lowering step.

From the test results of samples employing three types of carrier foils,carrier foil is considered to be easily peeled when HTE foil or standardelectrodeposited copper foil is employed as the carrier foil. The reasonfor the low peel strength is that the difference between the coefficientof thermal expansion of V-type copper foil serving as theelectrodeposited copper foil layer and that of carrier foil increaseswhen HTE foil or standard electrodeposited copper foil is employed asthe carrier foil instead of S-HTE foil. Since S-HTE foil isrecrystallized at approximately 180° C., the S-HTE foil easily followsthe thermal expansion behavior of the electrodeposited copper foil layerduring heating as compared with HTE foil. Thus, peeling at the organicadhesive interface layer is considered to be suppressed. Briefly, thegreater the difference in coefficient of thermal expansion, the moreeasily peeling occurs due to thermal expansion.

The above-shown data are typical data among the data which the presentinventors have obtained in their research. Thus, electrodeposited copperfoils with carrier which are formed of the materials satisfying theabove conditions can exhibit a peel strength of 3 gf/cm to 100 gf/cm;i.e., the target peel strength of the present invention, afterhot-pressing for producing copper-clad laminates is completed. Inaddition, the present inventors have carried out further experiments,and have found that when the average difference between the coefficientof thermal expansion of the electrodeposited copper foil layer at acertain temperature and that of the carrier foil layer at the sametemperature in the temperature-elevating step is 0.04×10⁻⁵/deg.C ormore, the target peel strength of the carrier foil can be attained.

Thus, when electrodeposited copper foil belonging to any one of Grades 1to 3 is employed as the carrier foil and V-type foil is employed as theelectrodeposited copper, the average difference between the coefficientof thermal expansion of the electrodeposited copper foil layer at acertain temperature and that of the carrier foil layer at the sametemperature becomes 0.04×10⁻⁵/deg.C or more. As a result, the carrierfoil can be peeled at a peel strength of 3 gf/cm to 100 gf/cm afterhot-pressing for producing copper-clad laminates is completed.

In the present invention, at least one species selected fromnitrogen-containing organic compounds, sulfur-containing organiccompounds, and carboxylic acids is preferably employed as the organicagent. The specific organic agents described below are suitably used inthe present invention. At present, it is confirmed that these compoundsare not detrimental to production of printed wiring boards from producedcopper-clad laminates including steps such as resist-application steps,etching steps, plating steps, and mounting steps.

Among these compounds, the nitrogen-containing organic compounds mayhave a substituent. Specifically, substituted triazloes are preferablyused. Examples include 1,2,3-benzotriazole (hereinafter referred to asBTA), carboxybenzotriazole (hereinafter referred to as CBTA), N′,N′-bis(benzotriazolylmethyl) urea (hereinafter referred to as BTD-U),1H-1,2,4-triazole (hereinafter referred to as TA), and3-amino-1H-1,2,4-triazole (hereinafter referred to as ATA).

Examples of preferably employed sulfur-containing compounds includemercaptobenzothiazole (hereinafter referred to as MBT), thiocyanuricacid (hereinafter referred to as TCA), and 2-benzimidazolethiol(hereinafter referred to as BIT).

Monocarboxylic acids are particularly preferably used as the carboxylicacids. Examples include oleic acid, linoleic acid, and linolenic acid.

Throughout the description, the term “electrodeposited copper foil(electrodeposited copper foil layer)” refers to an electrodepositedcopper foil coated with copper microparticles for anchoring and ananti-corrosion layer as shown in the cross-sectional view of FIG. 2. Thecopper microparticles form a surface-treated layer which ensures stableadhesion between an insulating substrate and a bulk copper layer formaintaining electrical conductivity of the produced printed wiringboards. However, in the present description, detailed description of thesurface-treated layer is omitted in the parts other than “Modes forCarrying Out the Invention.”

The aforementioned electrodeposited copper foil with carrier is producedby a method including forming an organic adhesive interface layer on acarrier foil by use of an organic agent and electrodepositing copperserving as an electrodeposited copper foil layer.

In the invention, there is provided a copper-clad laminate which isproduced from an electrodeposited copper foil with carrier. The carrierfoil of the copper-clad laminate can be peeled readily and smoothly byconsiderably low peeling force, thereby further enhancing operationalefficiency. In addition, the carrier foil can be peeled stably at 3gf/cm to 100 gf/cm, thereby attaining automated peeling operation bymeans of a peeling machine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an electrodeposited copperfoil with carrier according to the present invention; and

FIG. 2 is a schematic cross-sectional view of an apparatus used forproducing an electrodeposited copper foil with carrier according to thepresent invention.

MODES FOR CARRYING OUT THE INVENTION

Embodiments for carrying out the present invention will next bedescribed. In the following embodiments, methods for producing theelectrodeposited copper foil with carrier of the present invention andcopper-clad laminates produced from the electrodeposited copper foilwith carrier are described, along with results of evaluation of thefoils. The carrier foil described in the following embodiments is formedof an electrodeposited copper foil. In the Figures, when possible,identical portions are denoted by the same reference numerals. Theembodiments will be described with reference to FIGS. 1 and 2.

EMBODIMENT 1

In Embodiment 1, an electrodeposited copper foil with carrier 1 shown inFIG. 1 is described. An apparatus 2 for producing an electrodepositedcopper foil with carrier 1 is shown in FIG. 2. In the apparatus, acarrier foil 3 is unwound from a foil roll and travels, in a windingmanner, along the process line. An HTE foil which has a thickness of 18μm, is classified as Grade 3, and had not been subjected to any surfacetreatment was employed as the carrier foil 3, and the electrodepositedcopper foil layer 5 having a thickness of 3 μm was formed on a shinyside 4 of the carrier foil. Hereinafter, production conditions ofelectrodeposited copper foils with carrier will be described withreference to an apparatus wherein a variety of baths are continuouslydisposed in-line.

Firstly, the carrier foil 3 taken from the foil roll was transferredinto a pickling bath 6 filled with a diluted sulfuric acid solutionhaving a concentration of 150 g/l at 30° C. The carrier foil wasimmersed for 30 seconds, to remove oily matter and surface oxide filmfrom the surface of the carrier foil 3.

After the carrier foil 3 had been treated in the pickling bath 6, thefoil was transferred into an adhesive-interface-forming bath 7 filledwith a 5 g/l aqueous solution of CBTA (pH 5) at 40° C. The carrier foil3 was run into the bath and immersed for 30 seconds, forming a CBTAadhesive interface layer 8 on a surface of the carrier foil 3.

After the adhesive interface layer 8 had been formed, a bulk copperlayer 9 was formed from an electrolyte for electrodeposited copper foilof V-type on the adhesive interface layer. A bulk-copper-layer-formingbath 10 was filled with a copper sulfate solution having a sulfuric acidconcentration of 70 g/l and a copper concentration of 63.5 g/l(CuSO₄.5H₂O) at 40° C. While the carrier foil 3 having an adhesiveinterface layer 8 passes through the bath, the bulk copper layer 9 iselectrodeposited. In order to deposit copper uniformly and smoothly onthe adhesive interface layer, as shown in FIG. 2, anode plates 11 wereplaced such that the anode plates faced in parallel with one surface ofthe carrier foil 3. Electrolysis was carried out for 150 seconds underlevel plating conditions and at a current density of 5 A/dm². In thiscase, at least one tension roll 12 maintaining contact with the runningcarrier foil 3 served as a current-supplier so as to polarize thecarrier foil 3 per se to a cathode.

After formation of the bulk copper layer 9 was completed, the carrierfoil 3 was transferred into a copper-microparticle-forming bath 14 inorder to form copper microparticles 13 on the surface of the bulk copperlayer 9. The treatment carried out in the copper-microparticle-formingbath 14 involves depositing copper microparticles 13 on the bulk copperlayer 9 (step 14A) and seal-plating so as to prevent release of thecopper microparticles 13 (step 14B).

Step 14A, depositing copper microparticles 13 on the bulk copper layer9, employed a copper sulfate solution (sulfuric acid concentration of100 g/l, copper concentration of 18 g/l, temperature of 25° C.) similarto that employed in the bulk-copper-layer-forming bath 10, andelectrolysis was carried out for 10 seconds under conditions for formingburnt deposit at a current density of 10 A/dm². In this case, as shownin FIG. 2, anode plates 11 were placed such that the anodes plates facedthe bulk-copper-layer (9)-deposited surface of the carrier foil 3 inparallel.

Step 14B, seal-plating so as to prevent release of the coppermicroparticles 13, employed a copper sulfate solution (sulfuric acidconcentration of 150 g/l, copper concentration of 65 g/l, temperature45° C.) similar to that employed in the bulk-copper-layer-forming bath10, and electrolysis was carried out for 20 seconds under seal platingconditions and at a current density of 15 A/dm². In this case, as shownin FIG. 2, anode plates 11 were placed such that the anodes plates facedthe copper-microparticles (13)-deposited surface of the carrier foil 3in parallel.

Anti-corrosion treatment was carried out in an anti-corrosion-treatmentbath 15, by use of zinc as a corrosion-inhibiting element. Theconcentration of zinc in the anti-corrosion-treatment bath 15 wasmaintained by employment of zinc plates serving as soluble anodes 16.The electrolysis was carried out in a solution comprising zinc (20 g/l)and sulfuric acid (70 g/l), at a temperature of 40° C. and a currentdensity of 15 A/dm².

After completion of the anti-corrosion treatment, the carrier foil 3 waspassed through, over 40 seconds, a drying portion 17 where theatmosphere had been heated to 110° C., to thereby produce anelectrodeposited copper foil with carrier 1, which was then wound into aroll. During the aforementioned steps, the carrier foil ran at 2.0m/minute. The foil was then washed with water in a rinsing bath 18capable of performing about 15 sec. rinsing and disposed betweensuccessive operation baths, thereby preventing the solution from beingcarried over from the previous bath.

The thus-formed electrodeposited copper with carrier 1 and two sheets ofFR-4 prepreg having a thickness of 150 μm were laminated to therebyproduce a double-sided copper-clad laminate. The peel strength at theorganic adhesive interface 8 between the carrier foil layer 3 and theelectrodeposited copper foil layer 5 was measured. The results show thatthe adhesive interface layer 8 has an average thickness of 10 nm andthat the difference between the coefficient of thermal expansion of thecarrier foil layer 3 and that of the electrodeposited copper foil 5 is0.286×10⁻⁵/deg.C. The measured peel strength was 4.0 gf/cm (beforeheating) and 4.2 gf/cm (after one hour's heating at 180° C.).

EMBODIMENT 2

In Embodiment 2, an electrodeposited copper foil with carrier 1 shown inFIG. 1 is described. An apparatus 2 for producing an electrodepositedcopper foil with carrier 1 is shown in FIG. 2. In the apparatus, acarrier foil 3 is unwound from a foil roll and travels, in a windingmanner, along the process line. An S-HTE foil which has a thickness of18 μm, is classified as Grade 3, and had not been subjected to anysurface treatment was employed as a drum foil; i.e., the carrier foil 3,and the electrodeposited copper foil layer 5 having a thickness of 3 μmwas formed on a shiny surface 4 of the drum foil.

In Embodiment 2, the procedure of Embodiment 1 was carried out, exceptthat a different type of carrier foil was employed. Thus, repeateddescription is omitted.

The formed electrodeposited copper with carrier 1 and two sheets of FR-4prepreg having a thickness of 150 μm were laminated to thereby produce adouble-sided copper-clad laminate. The peel strength at the organicadhesive interface 8 between the carrier foil layer 3 and theelectrodeposited copper foil layer 5 was measured. The results show thatthe adhesive interface layer 8 has an average thickness of 10 nm andthat the difference between the coefficient of thermal expansion of thecarrier foil layer 3 and that of the electrodeposited copper foil 5 is0.046×10⁻⁵/deg.C. The measured peel strength was 70.4 gf/cm (beforeheating) and 70.8 gf/cm (after one hour's heating at 180° C.).

EMBODIMENT 3

In Embodiment 3, an electrodeposited copper foil with carrier 1 shown inFIG. 1 is described. An apparatus 2 for producing an electrodepositedcopper foil with carrier 1 is shown in FIG. 2. In the apparatus, acarrier foil 3 is unwound from a foil roll and travels, in a windingmanner, along the process line. A standard copper foil which has athickness of 18 μm, is classified as Grade 1, and had not been subjectedto any surface treatment was employed as a drum foil; i.e., the carrierfoil 3, and the electrodeposited copper foil layer 5 having a thicknessof 3 μm was formed on a shiny surface 4 of the drum foil.

In Embodiment 3, the procedure of Embodiment 1 was carried out, exceptthat a different type of carrier foil was employed. Thus, repeateddescription is omitted.

The formed electrodeposited copper with carrier 1 and two sheets of FR-4prepreg having a thickness of 150 μm were laminated to thereby produce adouble-sided copper-clad laminate. The peel strength at the organicadhesive interface 8 between the carrier foil layer 3 and theelectrodeposited copper foil layer 5 was measured. The results show thatthe adhesive interface layer 8 has an average thickness of 10 nm andthat the difference between the coefficient of thermal expansion of thecarrier foil layer 3 and that of the electrodeposited copper foil 5 is0.225×10⁻⁵/deg.C. The measured peel strength was 5.8 gf/cm (beforeheating) and 6.5 gf/cm (after one hour's heating at 180° C.).

Effects of the Invention

In the electrodeposited copper foil with carrier of the presentinvention, peeling at the interface between the carrier foil layer andthe electrodeposited copper foil layer can be readily performed at forcein the range of 3 gf/cm to 100 gf/cm. Thus, there can be attained stablepeelability of the carrier foil that conventional electrodepositedcopper foils with peelable carrier have never provided. Suchcharacteristics enable the carrier foil to be peeled automatically, andproduction yield of copper-clad laminates can be greatly improved.

What is claimed is:
 1. An electrodeposited copper foil with carriercomprising a carrier foil layer, an organic adhesive interface layerformed on the carrier foil layer, and an electrodeposited copper foillayer formed on the organic adhesive interface layer, wherein thematerial that forms the carrier foil layer is an electrodeposited copperfoil classified as Grades 1 to 3 of the IPC standards, and the materialthat forms the electrodeposited copper foil layer is classified as verylow profile type (V type) of the IPC standards, wherein the differencebetween the coefficient of thermal expansion of material forming thecarrier foil layer at a certain temperature and that of material formingthe electrodeposited copper foil at the same temperature is 4×10⁻⁷/° C.or more.
 2. A copper-clad laminate which is produced from anelectrodeposited copper foil with carrier as recited in claim 1.